Transmit diversity apparatus and method using two or more antennas

ABSTRACT

A transmit diversity system having at least four antennas. A first adder adds a first spread signal obtained by spreading a first symbol pattern with a first orthogonal code to a second spread signal obtained by spreading the first symbol pattern with a second orthogonal code, and transmits the added signal through a first antenna. A second adder adds the first spread signal to a third spread signal obtained by spreading an inverted symbol pattern of the first symbol pattern with the second orthogonal code, and transmits the added signal through a second antenna. A third adder adds a fourth spread signal obtained by spreading a second symbol pattern with the first orthogonal code to a fifth spread signal obtained by spreading the second symbol pattern with the second orthogonal code, and transmits the added signal through a third antenna. A fourth adder adds the fourth spread signal to a sixth spread signal obtained by spreading an inverted symbol of the second symbol pattern with the second orthogonal code, and transmits the added signal through a fourth antenna.

PRIORITY

This application claims priority to an application entitled “TransmitDiversity Apparatus and Method Using Two or More Antennas” filed in theKorean Industrial Property Office on Aug. 22, 2000 and assigned SerialNo. 2000-48722, the contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a transmit diversity system,and in particular, to a system in which a UTRAN supporting an N-antennatransmission diversity scheme is compatible with a UE for providing anM-antenna transmit diversity system.

2. Description of the Related Art

As mobile telecommunication technology progresses rapidly resulting inan increase of the amount of service data that can be accommodated, a3^(rd) generation mobile telecommunication system has been developed forhigh-speed data transmission. The 3^(rd) generation mobiletelecommunication system has been separately standardized into anasynchronous W-CDMA (Wideband Code Division Multiple Access) or UMTS(Universal Mobile Telecommunication System) system in Europe and asynchronous CDMA-2000 system in North America. Such a mobiletelecommunication system is generally configured such that a pluralityof UEs (User Equipments) communicate with one another through one UTRAN(UMTS Terrestrial Radio Access Network). In the mobile telecommunicationsystem, a received signal is subject to phase distortion due to fadingwhich occurs in a radio channel during high-speed data transmission. Thefading causes attenuation in amplitude of the received signal fromseveral dB to several tens of dB. If not properly compensated for duringdata demodulation, the phase of the received signal, distorted by thefading, becomes a cause of an information error on the data transmittedfrom a transmission side, decreasing the quality of service (QoS) of themobile telecommunication system. In order to transmit the high-speeddata without deterioration of the service quality, the mobiletelecommunication system must resolve the fading problem and to do so,employs various diversity techniques.

In general, the CDMA system adopts a Rake receiver, which performsdiversity receiving using delay spread of a channel. Although the Rakereceiver performs receive diversity for receiving a multi-path signal, adiversity technique using the above-stated delay spread does not operatedesirably when the delay spread is less than a preset value. Inaddition, a time diversity technique using interleaving and coding isused in a Doppler spread channel. However, it is difficult to use thetime diversity technique in a low-speed Doppler spread channel.

Therefore, in order to resolve the fading problem, a space diversitytechnique is used in a low-delay spread channel such as an indoorchannel and in a low-speed Doppler spread channel such as a pedestrianchannel. The space diversity technique uses two or more transmit/receiveantennas. That is, when a signal transmitted through one antenna isattenuated due to the fading, the space diversity technique receives asignal transmitted through another antenna. The space diversity can beclassified into a receive diversity technique using a receive antennaand a transmit diversity technique using a transmit antenna. Althoughthe receive diversity technique is applied to the UE, it is difficult tomount a plurality of antennas on the UE, taking into account the sizeand cost of the UE. Therefore, it is recommended to use the transmitdiversity technique in which a plurality of antennas are mounted on theUTRAN.

The transmit diversity technique relates to an algorithm for obtaining adiversity gain by receiving a downlink signal, and is divided into anopen loop mode and a closed loop mode. In the open loop mode, the UTRANtransmits a data signal through the diversity antennas after encoding,and the UE then receives the signal transmitted from the UTRAN anddecodes the received signal, thereby obtaining a diversity gain. In theclosed loop mode, (1) the UE predicts channel environments to which thesignals transmitted through the respective transmission antennas of theUTRAN will be subjected, (2) the UE calculates weights that are properto maximize power of the received signals, for the antennas of the UTRANdepending on the predicted values and transmits information on thecalculated weights to the UTRAN through an uplink and (3) the UTRAN thencontrols weights of the respective antennas based on the weightinformation transmitted from the UE. For channel measurement of the UE,the UTRAN transmits pilot signals assigned to the respective antennas,and the UE measures the channels through the pilot signals anddetermines optimal weights using this channel information.

U.S. Pat. No. 5,634,199, entitled “Method of Subspace Beamforming UsingAdaptive Transmitting Antennas with Feedback” and U.S. Pat. No.5,471,647, entitled “Method for Minimizing Cross-talk in AdaptiveAntennas”, disclose a method for using the transmit diversity techniquein a feedback mode. U.S. Pat. No. 5,634,199 discloses a channelmeasurement and feedback method using a perturbation algorithm and again matrix. However, this method, being a blind algorithm, is not usedoften since it has a low conversion speed for channel measurement andhas a difficulty in finding correct weights.

Meanwhile, UMTS, i.e., W-CDMA (3GPP (3^(rd) Generation PartnershipProject)) Release 99 recommends a method for quantizing weights of twoantennas and feeding back the quantized weights. This method refers to acase where there exists only the UE supporting two-antenna transmitdiversity techniques. That is, the W-CDMA Release 99 does not mention atransmission method for the case where the UTRAN has four transmitantennas, nor a UTRAN signal transmission method and a signal receptionmethod of the UE, considering the case where there coexists one UEemploying two-antenna transmit diversity techniques and another UEemploying four-antenna transmit diversity techniques. If the transmitantennas are expanded to four in number using a method for expanding theconventional method for transmitting a signal through a single antennato a method for transmitting a signal through two transmit antennas, theUE employing the two-antenna transmit diversity techniques will notoperate normally. If one method for transmitting a signal with twoantennas and another method for transmitting a signal with four antennasare both used to resolve the above-stated problem, a new problem ofpower imbalance between the antennas will arise.

A method for transmitting different pilot signals through a plurality ofantennas includes a time division multiplexing (TDM) system, a frequencydivision multiplexing (FDM) system and a code division multiplexing(CDM) system. To transmit the different pilot signals through theantennas, the W-CDMA system can use scrambling codes, channelizationcodes or orthogonal pilot symbol patterns.

In general, the system using two transmit antennas can obtain aconsiderably high diversity gain and a signal-to-noise ratio (SNR) of upto 3 dB, compared with existing systems using a single antenna. Inaddition, when the transmit diversity technique uses more than twoantennas, the diversity gain increases to a level higher than thediversity gain obtainable by the two-antenna transmit diversitytechnique, and the SNR also increases in proportion to the number ofantennas. Here, the increased diversity gain is relatively lower thanthe diversity gain obtained by the two-antenna diversity technique, buta diversity degree increases so that an increase in the signal-to-noiseratio (Eb/No) causes an increase in the diversity gain.

The W-CDMA Release 99 for the UMTS system currently discloses a transmitdiversity technique using only two antennas. However, the W-CDMA Release99 considers a necessity of a transmit diversity technology using morethan two antennas. That is, it must consider a mobile communicationsystem in which there coexists an existing UE receiving signalstransmitted from two transmit antennas and a UE receiving signalstransmitted from more than two transmit antennas. In this case, atransceiver is required which is structured such that the UE usingtwo-antenna transmit diversity technique and the UE using themore-than-two-antenna transmit diversity technique can normally receivesignals from the UTRAN. That is, a transmitting/receiving method andapparatus must be considered, which operates normally even when the UEdesigned to accommodate a UTRAN system employing the two-antennatransmit diversity technique is located in a service area of a UTRANsystem employing the more-than-two-antenna transmit diversity technique.On the other hand, a transmitting/receiving method and apparatus must bealso considered, which operates normally even when the UE designed toaccommodate the UTRAN system employing the more-than-two-antennatransmit diversity technique is located in a service area of the UTRANsystem employing the two-antenna transmit diversity technique. Inaddition, it is necessary to provide compatibility with the UE designedto accommodate the UTRAN system employing the transmit diversitytechnique using more than two antennas, without modification of the UEdesigned to accommodate the UTRAN system employing the two-antennatransmit diversity technique.

Compatibility is especially required in the common pilot channel, and acommon channel for transmitting common data. This is because although adedicated channel may transmit signals in a proper diversity methoddepending upon the characteristic and version of the UE, a common pilotchannel (CPICH) and a common data channel, which are common channels,must be constructed so as to support both a lower-version UE operatingin the UTRAN system employing the existing two-antenna transmitdiversity technique and an upper-version UE operating in the UTRANsystem employing the more-than-two-antenna transmit diversity technique.That is, the common channels must have higher reliability for thesignals transmitted by the system, compared with the dedicated channel,so that the common channels transmit the signals at higher powercompared with the dedicated channel. Therefore, it is possible toperform communication at lower transmission power by obtaining atransmit diversity gain from the common channels, thereby increasing anoverall system capacity, i.e., the number of subscribers.

The transmit antenna system is a system which transmits signals with aplurality of antennas. A transmission RF system including an antennapower amplifier, e.g., a low noise amplifier (LNA) is advantageous interms of cost and efficiency, when power of the signals transmittedthrough a plurality of antennas is uniformly distributed. If thetransmission power is non-uniformly distributed to a specific antenna,it is difficult to design the antenna and the cost increasesundesirably. It is difficult to provide the compatibility with themethod and apparatus employing the two-antenna transmit diversitytechnique, if the transmission/reception system is not efficientlydesigned.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a methodand apparatus for transmitting a signal in a UTRAN employing amore-than-two-antenna transmit diversity technique.

It is another object of the present invention to provide a method andapparatus for receiving a signal in a UE which receives signalstransmitted from a UTRAN employing a more-than-two-antenna transmitdiversity technique.

It is further another object of the present invention to provide amethod and apparatus for transmitting a pilot signal in a systememploying a transmit diversity technique using a different number ofantennas.

It is yet another object of the present invention to provide a methodand apparatus for receiving a pilot signal in a system employing atransmit diversity technique using a different number of antennas.

It is still another object of the present invention to provide a methodand apparatus for transmitting a pilot signal in a system employing atransmit diversity technique using antennas, the number of which is amultiple of four, by separating an orthogonal code and a scramblingcode.

It is still another object of the present invention to provide a methodand apparatus for receiving a pilot signal in a system employing atransmit diversity technique using antennas, the number of which is amultiple of four, by separating an orthogonal code and a scramblingcode.

It is still another object of the present invention to provide a methodand apparatus for transmitting a pilot signal in a system employing atransmit diversity technique using various numbers of antennas bylimiting signal transmission through a specific antenna in a transmitdiversity system having antennas, the number of which is a multiple offour.

It is still another object of the present invention to provide a methodand apparatus for receiving a pilot signal in a system employing atransmit diversity technique using various numbers of antennas bylimiting signal transmission through a specific antenna in a transmitdiversity system having antennas, the number of which is a multiple offour.

It is still another object of the present invention to provide a signaltransmission method and apparatus for distributing different power torespective antennas in a transmit diversity technique using a pluralityof antennas.

To achieve the above and other objects, there is provided a UTRANtransmitter in a mobile communication system having at least fourantennas. A first adder adds a first spread signal obtained by spreadinga first symbol pattern with a first orthogonal code after transmissionpower control, to a second spread signal obtained by spreading the firstsymbol pattern with a second orthogonal code being orthogonal with thefirst orthogonal code after transmission power control, and transmitsthe added signal through a first antenna. A second adder adds the firstspread signal to a third spread signal obtained by spreading a firstinverted symbol pattern obtained by phase-inverting the first symbolpattern with the second orthogonal code after transmission powercontrol, and transmits the added signal through a second antenna. Athird adder adds a fourth spread signal obtained by spreading a secondsymbol pattern being orthogonal with the first symbol pattern with thefirst orthogonal code after transmission power control, to a fifthspread signal obtained by spreading the second symbol pattern with thesecond orthogonal code after transmission power control, and transmitsthe added signal through a third antenna. A fourth adder adds the fourthspread signal to a sixth spread signal obtained by spreading a secondinverted symbol pattern obtained by phase-inverting the second symbolpattern with the second orthogonal code after transmission powercontrol, and transmits the added signal through a fourth antenna.

For transmission power control, the UTRAN multiplies the symbol patternsby a gain constant in order to enable receivers for receiving thetransmitted signals to have the same cell radius.

Preferably, the symbol pattern is a pilot symbol pattern or a datasymbol pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates a structure of a general four-antenna transmitdiversity system;

FIG. 2 illustrates a structure of a four-antenna transmit diversitysystem according to an embodiment of the present invention;

FIG. 3 illustrates a structure of a transmit diversity transmitter fortransmitting a pilot signal according to an embodiment of the presentinvention;

FIG. 4 illustrates a structure of a transmit diversity transmitter forpilot gain-controlled transmission according to another embodiment ofthe present invention;

FIG. 5 illustrates a structure of an eight-antenna transmit diversitytransmitter for transmitting a pilot signal according to anotherembodiment of the present invention;

FIG. 6 illustrates a structure of a transmit diversity receiver forpilot estimation according to another embodiment of the presentinvention;

FIG. 7 illustrates a structure of a transmit diversity receiver forpilot gain-controlled estimation according to another embodiment of thepresent invention;

FIG. 8 illustrates a receiver structure supporting an eight-antennatransmit diversity according to another embodiment of the presentinvention;

FIG. 9 illustrates a structure of a transmit diversity transmitter fortransmitting common data according to another embodiment of the presentinvention;

FIG. 10 illustrates a structure of a transmit diversity transmitter fortransmitting common channel data using a single orthogonal codeaccording to another embodiment of the present invention;

FIG. 11 illustrates a structure of a transmit diversity receiver forestimating common channel data using two orthogonal codes according toanother embodiment of the present invention; and

FIG. 12 illustrates a structure of a transmit diversity receiver forestimating common data using a single orthogonal code according toanother embodiment of the present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail since they would obscure the invention in unnecessary detail.

FIG. 1 illustrates a structure of a general four-antenna transmitdiversity system. Referring to FIG. 1, a UTRAN (UMTS Terrestrial RadioAccess Network) 101 includes four antennas ANT#1–ANT#4, and transmits auser signal through the four antennas after converting the user signalto be proper for four-antenna transmission. A UE 103 receives a signaltransmitted through the first antenna ANT#1 over an h₁ channel, a signaltransmitted through the second antenna ANT#2 over an h₂ channel, asignal transmitted through the third antenna ANT#3 over an h₃ channel,and a signal transmitted through the fourth antenna ANT#4 over an h₄channel, respectively. The UE 103 decodes the signals received from thefour antennas ANT#1–ANT#4 of the UTRAN 101 into original transmissiondata through a demodulating process.

FIG. 2 illustrates a structure of a four-antenna transmit diversitysystem according to an embodiment of the present invention, wherein a UEsupporting the two-antenna transmit diversity technique receives fourpilot signals transmitted from a UTRAN. Referring to FIG. 2, a UE 203supporting the two-antenna transmit diversity technique receives thepilot signals from the four antennas of a UTRAN 201 in such a mannerthat it receives the pilot signals effectively from two antennas.Specifically, the UE 203 receives a pilot signal transmitted throughfirst and second antennas ANT#1 and ANT#2 of the UTRAN 201 over an h_(A)channel, and receives a pilot signal transmitted through third andfourth antennas ANT#3 and ANT#4 over an h_(B) channel.

In the case where the UE supporting the two-antenna transmit diversitytechnique exists in a service area of the UTRAN supporting thefour-antenna transmit diversity technique as shown in FIG. 2, atransmitter of the UTRAN 201 employing the four-antenna transmitdiversity has the structure shown in FIG. 3.

FIG. 3 illustrates a structure of a transmit diversity transmitter fortransmitting a pilot signal according to an embodiment of the presentinvention. The pilot signals output from four antennas shown in FIG. 3can be represented by Equations (1) to (4), respectively. That is,Equation (1) represents an output x₁(t) of a first antenna 347, andEquation (2) represents an output x₂(t) of a second antenna 349.Further, Equation (3) represents an output x₃(t) of a third antenna 351,and Equation (4) represents output x₄(t) of a fourth antenna 353.x ₁(t)=p ₁(t)×(g·C _(OVSF1)(t)+C _(OVSF2)(t))×C _(SC)(t)  (1)x ₂(t)=p ₁(t)×(g·C _(OVSF1)(t)−C _(OVSF2)(t))×C _(SC)(t)  (2)x ₃(t)=p ₂(t)×(g·C _(OVSF1)(t)+C _(OVSF2)(t))×C _(SC)(t)  (3)x ₄(t)=p ₂(t)×(g·C _(OVSF1)(t)−C _(OVSF2)(t))×C _(SC)(t)  (4)

In Equations (1) to (4), p₁(t) indicates a pilot symbol pattern 301 inthe form of AA which is a first symbol pattern, and p₂(t) indicates apilot symbol pattern 303 n the form of A-A or -AA which is a secondsymbol pattern. The first symbol pattern in the form of AA is orthogonalwith the second symbol pattern in the form of A-A or -AA, so that anorthogonal property between the pilot symbol pattern 301 and the pilotsymbol pattern 303 is maintained. Further, C_(OVSF1)(t) and C_(OVSF2)(t)indicate a first orthogonal code OVSF1 (305) and a second orthogonalcode OVSF2 (315), respectively, which are Walsh codes or OVSF(Orthogonal Variable Spreading Factor) codes for spreading the pilotsymbol patterns 301 and 303. In addition, C_(SC)(t) indicates ascrambling code 337 having the same chip rate as that of the orthogonalcodes 305 and 315. Finally, ‘g’ indicates a gain constant 355 used toguarantee performance of the UE supporting the existing two-antennatransmit diversity technique.

A pilot signal ‘A’ to be transmitted by the UTRAN 201 through theantennas may have a value of 1 or −1, when it is applied to a BPSK(Binary Phase Shift Keying) transmitter, or may have a value of 1+j,when it is applied to a QPSK (Quadrature Phase Shift Keying)transmitter. Accordingly, the first pilot symbol pattern 301 in the formof AA is multiplied by the gain constant 355 by a multiplier 357 andthen multiplied by the first orthogonal code OVSF1 (305) by a multiplier307, and the resulting value is provided to an adder 329. For example,the first orthogonal code OVS1 has a length of 256 chips. Further, thefirst pilot symbol pattern 301 is multiplied by the second orthogonalcode OVSF2 by a multiplier 317, and then provided to the adder 329. Theadder 329 adds the output of the multiplier 307 to the output of themultiplier 317 and provides its output to a multiplier 339. The outputof the adder 329 is multiplied by the scrambling code 337 by themultiplier 339 and then transmitted through the first antenna 347.Further, the first pilot symbol pattern 301 is multiplied by the gainconstant 355 by the multiplier 357 and then multiplied by the firstorthogonal code OVSF1 (305) by the multiplier 307, and the resultingvalue is provided to an adder 331. Further, the first pilot symbolpattern 301 is multiplied by the second orthogonal code OVSF2 (315) bythe multiplier 317 and then multiplied by a signal of −1 by a multiplier325 for signal inversion, and the resulting value is provided to theadder 331. The adder 331 adds the output of the multiplier 307 to theoutput of the multiplier 325 and provides its output to a multiplier341. The output of the adder 331 is multiplied by the scrambling code337 by the multiplier 341 and then transmitted through the secondantenna 349. Although the multiplier 325 multiplies the input signal bythe signal of −1 for phase inversion, the phase inversion of the inputsignal can be performed at either an input stage or an output stage ofthe UTRAN transmitter.

Similarly, the second pilot symbol pattern 303 in the form of A-A or -AAis multiplied by the gain constant 355 by a multiplier 359 and thenmultiplied by the first orthogonal code OVS1 (305) by a multiplier 311,and the resulting value is provided to an adder 333. Further, the secondpilot symbol pattern 303 is multiplied by the second orthogonal codeOVSF2 by a multiplier 321, and then, provided to the adder 333. Theadder 333 adds the output of the multiplier 311 to the output of themultiplier 321 and provides its output to a multiplier 343. The outputof the adder 333 is multiplied by the scrambling code 337 by themultiplier 343 and then transmitted through the third antenna 351.Further, the second pilot symbol pattern 303 is multiplied by the gainconstant 355 by the multiplier 359 and then multiplied by the firstorthogonal code OVS1 (305) by the multiplier 311, and the resultingvalue is provided to an adder 335. Further, the second pilot symbolpattern 303 is multiplied by the second orthogonal code OVSF2 (315) bythe multiplier 321 and then multiplied by the signal of −1 by amultiplier 327 for signal inversion, and the resulting value is providedto the adder 335. The adder 335 adds the output of the multiplier 311 tothe output of the multiplier 327 and provides its output to a multiplier345. The output of the adder 335 is multiplied by the scrambling code337 by the multiplier 345 and then transmitted through the fourthantenna 353. Although the multiplier 327 multiplies the input signal bythe signal of −1 for phase inversion, the phase inversion of the inputsignal can be performed at either an input stage or an output stage ofthe UTRAN transmitter as described with reference to the multiplier 325.The adders 329, 331, 333 and 335 in the transmitter can be united into asingle adder. In addition, the multipliers 339, 341, 343 and 345 formultiplying their input signals by the scrambling code 337 can also beunited into a single multiplier, and can also perform complex spreading.The multipliers 325 and 327 for inverting their input signals bymultiplying them by the signal of −1 can be put in other places as longas the signals to be output through the second and fourth antennas 349and 353 are subjected to phase inversion. For example, the multiplier325 can be arranged in front of the multiplier 317 to inverse the inputpilot symbol pattern 301 or the input OVSF code 315. In addition, it isalso possible to remove the multiplier 325. In this case, the adder 331must subtract the output signal of the multiplier 317 from the outputsignal of the multiplier 307. In the same manner, the multiplier 327 canbe arranged in front of the multiplier 321 to inverse the input pilotsymbol pattern 303 or the input OVSF code 315. In addition, it is alsopossible to remove the multiplier 327. In this case, the adder 335 mustsubtract the output signal of the multiplier 321 from the output signalof the multiplier 311. If the gain constant 355 is g=1, it is notincluded in the hardware structure. In addition, the gain constant 355has a constant value or a variable value which can be adaptivelycontrolled according to a channel environment or a user environment in apreset unit (e.g., symbol unit, slot unit or frame unit).

FIG. 4 illustrates a structure of a transmit diversity transmitter forpilot gain-controlled transmission according to another embodiment ofthe present invention, wherein the pilot signals of the respectiveantennas are transmitted at different transmission power.

A method for controlling transmission power, i.e., gain of the pilotsignals transmitted through the respective antennas will be describedwith reference to FIG. 4. The reason for controlling transmission powerof the pilot signals transmitted through the respective antennas is tocontrol the cell radii of the respective receivers for receiving thepilot signals to be identical. Here, “controlling the cell radii of therespective receivers to be identical” refers to controlling the cellradii for the pilot signals to be identical regarding a receiveremploying a 1-antenna transmit diversity technique, a receiver employinga two-antenna transmit diversity technique, a receiver employing afour-antenna transmit diversity technique and a receiver employing atransmit diversity technique having a different number of antennas.

Referring to FIG. 4, when the UTRAN 201 outputs the pilot signals havingthe same transmission power, a signal transmitted through a firstantenna 347 is multiplied by a gain constant g1 (451), a signaltransmitted through a second antenna 349 is multiplied by a gainconstant g2 (453), a signal transmitted through a third antenna 351 ismultiplied by a gain constant g3 (455) and a signal transmitted througha fourth antenna 353 is multiplied by a gain constant g4 (457). Themethod for controlling transmission power, i.e., gains of the antennasby multiplying the signals transmitted through the respective antennasby the gain constants corresponding to the respective antennas can beapplied not only to the pilot signals but also to common data signalswhich will be described later. In addition, the method can be applied toany signal transmitted in the system employing the transmit diversitytechnique using a plurality of antennas, when it is necessary toindependently control the gains of the antennas.

The transmitter structure employing the four-antenna transmit diversitytechnique has been described with reference to FIGS. 3 and 4. Next, atransmitter structure supporting an eight-antenna transmit diversitytechnique will be described with reference to FIG. 5.

FIG. 5 illustrates a structure of an eight-antenna transmit diversitytransmitter for transmitting a pilot signal according to anotherembodiment of the present invention, wherein the structures used for thefour-antenna transmit diversity are arranged twice in parallel toimplement the eight-antenna transmit diversity. Referring to FIG. 5, amethod for transmitting pilot signals through first to fourth antennas347, 349, 351 and 353 is identical to the four-antenna transmitdiversity method described with reference to FIG. 3, so the detaileddescription will not be made. Although a scrambling code C_(SC1) isrepresented differently from the scrambling code C_(SC) shown in FIGS. 3and 4, it should be noted that they are the same scrambling codes. Thatis, since the four-antenna transmit diversity technique is expanded toan eight-antenna transmit diversity technique, the scrambling codeapplied to the first to fourth antennas 347, 349, 351 and 353 isrepresented by C_(SC1), while the scrambling codes applied to fifth toeighth antennas 589, 591, 593 and 595 is represented by C_(SC2). Forsimplicity, FIG. 5 does not show a gain control process for separatelycontrolling transmission power of the antennas and a process forindependently multiplying the pilot signals by the gain constants of theantennas.

As stated above, the eight-antenna transmit diversity technique can beimplemented by doubling the four-antenna transmit diversity. This can beachieved by further assigning two new orthogonal codes, i.e., a thirdorthogonal code OVSF3 (560) and a fourth orthogonal code OVSF4 (561) forthe pilot signals of the four additional antennas in addition to thefirst orthogonal code OVSF1 (305) and the second orthogonal code OVSF2(315) applied to the first to fourth antennas 347, 349, 351 and 353, orby further assigning a new scrambling code C_(SC2) (597) in addition tothe scrambling code C_(SC1) (337) applied to the first to fourthantennas 347, 349, 351 and 353 and then applying the first and secondorthogonal codes OVSF1 and OVSF2, instead of the third and fourthorthogonal codes OVSF3 and OVSF4, to the first to fourth antennas 347,349, 351 and 353. If the scrambling code C_(SC1) (337) is not identicalto the scrambling code C_(SC2) (597), the first orthogonal code OVSF1(305) is identical to the third orthogonal code OVSF3 (560) and thesecond orthogonal code OVSF2 (315) is also identical to the fourthorthogonal code OVSF4 (561). In contrast, if the first orthogonal codeOVSF1 (305) is not identical to the third orthogonal code OVSF3 (560)and the second orthogonal code OVSF2 (315) is not identical to thefourth orthogonal code OVSF4 (561), then the scrambling code C_(SC1)(337) is identical to the scrambling code C_(SC2) (597). By applying thedifferent codes to the antennas in this way, it is possible to apply thetransmit diversity technique to the fifth to eighth antennas 589, 591,593 and 595, thus making it possible to expand the number of antennas towhich the transmit diversity technique is applied. In addition, thenumber of antennas to which the transmit diversity technique is appliedcan be expanded in analogous manner by a multiple of four. When thenumber of antennas increases by four, the number of the requiredorthogonal codes also increases by two or one new scrambling code isadditionally used.

Of course, even in the case where the number of antennas used by thetransmit diversity technique is not a multiple of four, it is possibleto implement the invention by modifying the method for expanding thenumber of antennas to a multiple of four. For example, when the transmitdiversity uses three antennas, it is possible to implement thethree-antenna transmit diversity by not transmitting the signal outputfrom the last antenna, i.e., the fourth antenna 353 in the above-statedfour-antenna transmit diversity technique. As another example, when thetransmit diversity uses six antennas, it is possible to implement thesix-antenna transmit diversity technique by not transmitting the signalsoutput from the sixth and eighth antennas 591 and 595 in theeight-antenna transmit diversity technique.

Next, a structure of a UE receiver corresponding to the UTRANtransmitter shown in FIG. 3 will be described with reference to FIG. 6.FIG. 6 illustrates a structure of a transmit diversity receiver forestimating a pilot signal according to an embodiment of the presentinvention. Four output signals shown in FIG. 6 can be represented byEquations (5) to (8) below. Specifically, Equation (5) represents achannel measurement value ĥ₁ of the first antenna 347, and Equation (6)represents a channel measurement value ĥ₂ of the second antenna 349.Further, Equation (7) represents a channel measurement value ĥ₃ of thethird antenna 351, and Equation (8) represents a channel measurementvalue ĥ₄ of the fourth antenna 353.ĥ ₁ =∫r(t)·C _(SC)(t)·C _(OVSF1)(t){p ₁(t)+p ₂(t)}dt  (5)ĥ ₂ =∫r(t)·C _(SC)(t)·C _(OVSF1)(t){p ₁(t)−p ₂(t)}dt  (6)ĥ ₃ =∫r(t)·C _(SC)(t)·C _(OVSF2)(t){p ₁(t)+p ₂(t)}dt  (7)ĥ ₄ =∫r(t)·C _(SC)(t)·C _(OVSF2)(t){p ₁(t)−p ₂(t)}dt  (8)

In Equations (5) to (8), r(t) indicates a signal received at the UE 203through an antenna 401, p₁(t) indicates a first pilot symbol pattern413, and p₂(t) indicates a second pilot symbol pattern 423 which isorthogonal with the first pilot symbol pattern 413. In addition,C_(OVSF1)(t) indicates a first orthogonal code OVSF1 (407), C_(OVSF2)(t)indicates a second orthogonal code OVSF2 (411), and C_(SC)(t) indicatesa scrambling code 403. The pilot symbol patterns, the orthogonal codesand the scrambling code are identical to those used in the UTRAN and arepre-stored in the UE.

The signal r(t) received through the antenna 401 of the UE 203 isprovided to a despreader 405 after it is converted to a baseband signal,and then, despread in despreader 405 with the scrambling code 403. Thesignal despread by the despreader 405 is provided both to an orthogonaldespreader 408 and an orthogonal despreader 409. The orthogonaldespreader 408 despreads the signal output from the despreader 405 usingthe first orthogonal code OVSF1 (407) and the orthogonal despreader 409despreads the signal output from the despreader 405 using the secondorthogonal code OVSF2 (411). The signal despread with the firstorthogonal code OVSF1, output from the orthogonal despreader 408, isaccumulated by an accumulator (ACC) 440 in a symbol unit. The outputsignal of the accumulator 440 is multiplied by the first pilot symbolpattern 413 by a multiplier 415, and then accumulated by an accumulator425. Further, the output signal of the accumulator 440 is multiplied bythe second pilot symbol pattern 423 by a multiplier 417, and thenaccumulated by an accumulator 427.

In addition, the signal despread with the second orthogonal code OVSF2,output from the orthogonal despreader 409, is accumulated by anaccumulator 441 in a symbol unit. The output signal of the accumulator441 is multiplied by the first pilot symbol pattern 413 by a multiplier419, and then accumulated by an accumulator 429. Further, the outputsignal of the accumulator 441 is multiplied by the second pilot symbolpattern 423 by a multiplier 421, and then accumulated by an accumulator431.

The output signal of the accumulator 425 is added to the output signalof the accumulator 429 by an adder 433, and is output as the pilotsymbol pattern signal transmitted through the first antenna 347 of theUTRAN. The output signal of the accumulator 427 is added to the outputsignal of the accumulator 431 by an adder 435, and is output as thepilot symbol pattern signal transmitted through the second antenna 349of the UTRAN. The output signal of the accumulator 429 is subtractedfrom the output signal of the accumulator 425 by an adder 437, and isoutput as the pilot symbol pattern signal transmitted through the thirdantenna 351 of the UTRAN. The output signal of the accumulator 431 issubtracted from the output signal of the accumulator 427 by an adder439, and is output as the pilot symbol pattern signal transmittedthrough the fourth antenna 353 of the UTRAN.

When the transmitter independently controls the transmission power ofthe respective antennas using the associated gain constants as shown inFIG. 4, the receiver is required to control the transmission power ofthe respective antennas according to the associated gain constants. Areceiver structure for performing gain control for the transmissionpower control will be described with reference to FIG. 7.

FIG. 7 illustrates a structure of a transmit diversity receiver forpilot gain-controlled estimation according to another embodiment of thepresent invention, wherein if the signals transmitted through therespective antennas of the transmitter have different transmissionpower, the receiver performs exact pilot estimation by multiplying pilotestimation values by reciprocals of the gain constants used in thetransmitter. A gain constant 1/g₁ (711) which is a reciprocal of thegain constant g₁ (451) multiplied by the signal transmitted through thefirst antenna 347, a gain constant 1/g₃ (713) which is a reciprocal ofthe gain constant g₂ (453) multiplied by the signal transmitted throughthe second antenna 349, a gain constant 1/g₂ (715) which is a reciprocalof the gain constant g₃ (455) multiplied by the signal transmittedthrough the third antenna 351, and a gain constant 1/g₄ (717) which is areciprocal of the gain constant g₄ (457) multiplied by the signaltransmitted through the fourth antenna 353, are previously known to thereceiver by pre-storing the gains in accordance with the transmitter, orprovided to the UE by the transmitter as occasion demands. The receiverestimates exact pilot signals by multiplying pilot estimation values ofthe pilot signals received from the respective antennas by theassociated gain constants. Processes other than the process formultiplying the reciprocals of the gain functions are the same as theprocesses described in FIG. 6, so the detailed description will not begiven.

Further, a receiver corresponding to a transmitter supporting a transmitdiversity having antennas, the number of which is larger than four andis a multiple of four, e.g., the transmitter supporting theeight-antenna transmit diversity technique shown in FIG. 8, estimatesthe pilot symbols in the same manner as performed in the four-antennatransmit diversity method, using the new orthogonal codes or the newscrambling code used in the transmitter. A structure of the receivercorresponding to the transmitter employing the eight-antenna transmitdiversity technique will be described with reference to FIG. 8.

FIG. 8 illustrates a receiver structure supporting an eight-antennatransmit diversity according to another embodiment of the presentinvention, wherein the eight-antenna transmit diversity is implementedby doubling the four-antenna transmit diversity in parallel. Forestimation of the first 4 channels ĥ₁, ĥ₂, ĥ₃ and ĥ₄ of the signalreceived through the antenna 401 of the UE 203, the receiver primarilydespreads the received signal using the first scrambling code C_(SC1)(337) and then secondarily despreads the despread signal using the firstand second orthogonal codes OVSF1 (305) and OVSF2 (315). The signalsdespread with the first and second orthogonal codes OVSF1 (305) andOVSF2 (315) are accumulated by their associated accumulators (notshown). Processes other than the process for despreading the first 4channels ĥ₁, ĥ₂, ĥ₃ and ĥ₄ are the same as the processes performed inthe receiver supporting the four-antenna transmit diversity shown inFIG. 6, so the detailed description will not be given. In addition, aprocess for controlling the gain constants, required to describe thereceiver structure corresponding to the transmitter structure shown inFIG. 5, is also not described, for simplicity. If the transmittercontrols transmission power of the respective antennas using the gainconstants during transmission, the receiver requires an additionalprocess for controlling output signals by multiplying the respectivechannel estimation values by reciprocals of the gain constants used forpower control in the transmitter.

For pilot signal estimation on the next four channels ĥ₅, ĥ₆, ĥ₇ and ĥ₈followed by the first four channels ĥ₁, ĥ₂, ĥ₃ and ĥ₄, the receiverprimarily despreads the received signal using the second scrambling codeC_(SC2) (597) and then secondarily despreads the despread signal usingthe third and fourth orthogonal codes OVSF3 (560) and OVSF4 (561). Thesignals despread with the third and fourth orthogonal codes OVSF3 (560)and OVSF4 (561) are accumulated by their associated accumulators (notshown). Processes other than the process for despreading the next 4channels ĥ₅, ĥ₆, ĥ₇ and ĥ₈ are the same as the processes performed inthe receiver supporting the four-antenna transmit diversity shown inFIG. 6, so the detailed description will not be given. The gainconstants are not considered during signal estimation on the channelsĥ₅, ĥ₆, ĥ₇ and ĥ₈. If, however, the transmitter controls transmissionpower of the respective antennas using the gain constants duringtransmission, the receiver requires an additional process forcontrolling output signals by multiplying the respective channelestimation values by reciprocals of the gain constants used for powercontrol in the transmitter.

In addition, as described in FIG. 5, if the first scrambling codeC_(SC1) (337) is not identical to the second scrambling code C_(SC2)(597), the first orthogonal code OVSF1 (305) is identical to the thirdorthogonal code OVSF3 (560) and the second orthogonal code OVSF2 (315)is also identical to the fourth orthogonal code OVSF4 (561). Incontrast, if the first orthogonal code OVSF1 (305) is not identical tothe third orthogonal code OVSF3 (560) and the second orthogonal codeOVSF2 (315) is not identical to the fourth orthogonal code OVSF4 (561),then the first scrambling code C_(SC1) (337) is identical to the secondscrambling code C_(SC2) (597). Therefore, when the number of antennasincreases by four, the number of the required orthogonal codes alsoincreases by two or one new scrambling code must be additionally used inthe receiver corresponding to the transmitter employing the transmitdiversity technique.

The transmit diversity system for transmitting and receiving the pilotsymbol patterns according to the present invention has been describedwith reference to FIGS. 3 to 8. Next, a transmit diversity system fortransmitting and receiving common data symbol patterns together with thepilot symbol patterns will be described with reference to FIGS. 9 to 12.

FIG. 9 illustrates a structure of a transmit diversity transmitter fortransmitting common data according to anther embodiment of the presentinvention. Respective data outputs of four antennas shown in FIG. 9 canbe represented by Equations (9) to (12) below. Specifically, Equation(9) represents an output y₁(t) of a first antenna 547 and Equation (10)represents an output y₂(t) of a second antenna 549. Further, Equation(11) represents an output y₃(t) of a third antenna 551 and Equation (12)represents an output y₄(t) of a fourth antenna 553.[y ₁(2t)y ₁(2t+1)]=[s(2t)·C _(SC)(2t)s(2t+1)·C _(SC)(2t+1)]·(g·C_(OVSF1)(2t)+C _(OVSF2)(2t))  (9)[y ₂(2t)y ₂(2t+1)]=[s(2t)·C _(SC)(2t)s(2t+1)·C _(SC)(2t+1)]·(g·C_(OVSF1)(2t)−C _(OVSF2)(2t))  (10)[y ₃(2t)y ₃(2t+1)]=[−s*(2t+1)·C _(SC)(2t)s*(2t)·C _(SC)(2t+1)]·(g·C_(OVSF1)(2t)+C _(OVSF2)(2t))  (11)[y ₄(2t)y ₄(2t+1)]=[−s*(2t+1)·C _(SC)(2t)s*(2t)·C _(SC)(2t+1)]·(g·C_(OVSF1)(2t)−C _(OVSF2)(2t))  (12)

In Equations (9) to (12), [s(2t)s(2t+1)] indicates a 2-consecutive datasymbol pattern 501, and [−s*(2t+1)s*(2t)] indicates a 2-consecutivediversity data symbol pattern 503 which is orthogonal with the2-consecutive data symbol pattern 501. Further, C_(OVSF1)(t) andC_(OVSF2)(t) indicate a first orthogonal code OVSF1 (505) and a secondorthogonal code OVSF2 (515), respectively, which are Walsh codes or OVSF(Orthogonal Variable Spreading Factor) codes. In addition, C_(SC)(t)indicates a scrambling code 537, and ‘g’ indicates a gain constant 555used to guarantee performance of the UE supporting the existingtwo-antenna transmit diversity technique.

A data signal ‘A’ to be transmitted in the four-antenna transmitdiversity system may have a value of 1 or −1, when it is applied to aBPSK transmitter, and may have a value of {1+j, −1+j, 1−j, −1−j}, whenit is applied to a QPSK transmitter. The data signal can also be appliedto a transmitter supporting such high efficiency modulation as 8PSK(8-state Phase Shift Keying) modulation, 16 QAM (16-ary QuadratureAmplitude Modulation) modulation and 64 QAM (64-ary Quadrature AmplitudeModulation) modulation in the similar method. It will be assumed hereinthat the data signal ‘A’ is applied to an STTD (Space Time block codingbased Transmit Diversity) technique which is one of open loop modetechniques among the above-stated transmit diversity techniques. TheSTTD considers a dedicate physical channel (DPCH), a primary commoncontrol physical channel (P_CCPCH), a secondary common control physicalchannel (S_CCPCH), a synchronization channel (SCH), a page indicationchannel (PICH), an acquisition indication channel (AICH), and a physicaldownlink shared channel (PDSCH), and calculates channel estimationvalues of the respective antennas for STT decoding using a common pilotchannel (CPICH). In the case where the data signal ‘A’ has a format suchthat symbols S₁ and S₂ are sequentially received in transmit diversityencoding time intervals T₁ and T₂, respectively, the consecutive symbolsS₁S₂, after being subjected to STTD encoding, are output as S₁S₂ throughthe first antenna and as −S₂*S₁* through the second antenna.Specifically describing the symbol STTD encoding in a channel bit unit,if it is assumed that the symbols S₁ and S₂ received in the transmitdiversity encoding time intervals T₁ and T₂ as stated above are createdas channel bits b₀b₁ and b₂b₃, respectively, then the symbols S₁S₂ arereceived as channel bits b₀b₁b₂b₃. By performing STTD encoding on thechannel bits b₀b₁b₂b₃, the transmitter outputs channel bits b₀b₁b₂b₃(S₁S₂) through the first antenna and outputs channel bits −b₂b₃b₀−b₁(−S₂*S₁*) through the second antenna. Here, the first antenna is areference antenna and the second antenna is a diversity antenna.

Among the data symbol patterns created through the STTD encoding, thesymbols S₁S₂ transmitted through the first antenna being a referenceantenna will be referred to as a “reference antenna STTD code block 501”and the symbols −S₂*S₁* transmitted through the second antenna being adiversity antenna will be referred to as a “diversity antenna STTD codeblock 503”. The reference antenna STTD code block 501 is multiplied bythe gain constant g (555) by a multiplier 557, and then multiplied bythe first orthogonal code 505 by a multiplier 507. For example, thefirst orthogonal code OVSF1 (505) has a chip rate of 256. Further, thereference antenna STTD code block 501 is multiplied by the secondorthogonal code OVSF2 (515) by a multiplier 517. The output of themultiplier 517 is added to the output of the multiplier 507 by an adder529, and then multiplied by the scrambling code 537 by a multiplier 539.The output signal of the multiplier 539 is transmitted through the firstantenna 547. In addition, the reference antenna STTD code block 501 ismultiplied by the gain constant g (555) by the multiplier 557 and thenmultiplied by the first orthogonal code OVSF1 (505) by the multiplier507, and the resulting value is provided to an adder 531. Further, thereference antenna STTD code block 501 is multiplied by the secondorthogonal code OVSF2 (515) by the multiplier 517 and then multiplied bya signal of −1 by a multiplier 525 for signal inversion, and theresulting value is provided to the adder 531. The adder 531 adds theoutput of the multiplier 507 to the output of the multiplier 525 andprovides its output to a multiplier 541. The output of the adder 531 ismultiplied by the scrambling code 537 by the multiplier 541 and thentransmitted through the second antenna 549.

Similarly, the diversity antenna STTD code block 503 is multiplied bythe gain constant 555 by a multiplier 559 and then multiplied by thefirst orthogonal code OVSF1 (505) by a multiplier 511, and the resultingvalue is provided to an adder 533. Further, the diversity antenna STTDcode block 503 is multiplied by the second orthogonal code OVSF2 (515)by a multiplier 521, and then, provided to the adder 533. The adder 533adds the output of the multiplier 511 to the output of the multiplier521 and provides its output to a multiplier 543. The output of the adder533 is multiplied by the scrambling code 537 by the multiplier 543 andthen transmitted through the third antenna 551. Further, the diversityantenna STTD code block 503 is multiplied by the gain constant 555 bythe multiplier 559 and then multiplied by the first orthogonal codeOVSF1 (505) by the multiplier 511, and the resulting value is providedto an adder 535. Further, the diversity antenna STTD code block 503 ismultiplied by the second orthogonal code OVSF2 (515) by the multiplier521 and then multiplied by the signal of −1 by a multiplier 527 forsignal inversion, and the resulting value is provided to the adder 535.The adder 535 adds the output of the multiplier 511 to the output of themultiplier 527 and provides its output to a multiplier 545. The outputof the adder 535 is multiplied by the scrambling code 537 by themultiplier 545 and then transmitted through the fourth antenna 553. Inthe transmitter, the adders 529, 531, 533 and 535 can be united into asingle adder. In addition, the multipliers 539, 541, 543 and 545 formultiplying their input signals by the scrambling code 537 can also beunited into a single multiplier, and can also perform complex spreading.The multipliers 525 and 527 for inverting their input signals bymultiplying them by the signal of −1 can be put in other places as longas the signals to be output through the second and fourth antennas 549and 553 are subjected to phase inversion. For example, the multiplier525 can be arranged in front of the multiplier 517 to invert the inputdata symbol pattern 501 or the input OVSF code 515. In addition, it isalso possible to remove the multiplier 525. In this case, the adder 531must subtract the output signal of the multiplier 517 from the outputsignal of the multiplier 507. In the same manner, the multiplier 527 canbe arranged in front of the multiplier 521 to invert the input datasymbol pattern 503 or the input OVSF code 515. In addition, it is alsopossible to remove the multiplier 527. In this case, the adder 535 mustsubtract the output signal of the multiplier 521 from the output signalof the multiplier 511. If the gain constant 555 is g=1, it is notincluded in the hardware structure. In addition, the gain constant 555has a constant value or a variable value which can be adaptivelycontrolled in a symbol unit according to a channel environment or a userenvironment.

The four-antenna transmit diversity transmitter for transmitting thecommon channel data symbols using two orthogonal codes has beendescribed with reference to FIG. 9. A simplified four-antenna transmitdiversity transmitter for transmitting the common channel data symbolsusing a single orthogonal code will be described with reference to FIG.10.

FIG. 10 illustrates a structure of a transmit diversity transmitter fortransmitting common channel data using a single orthogonal codeaccording to another embodiment of the present invention. In FIG. 10,among the data symbol patterns created through the STTD encoding, thesymbols S₁S₂ transmitted through first and second antennas 5047 and 5049serving as reference antennas will be referred to as a “referenceantenna STTD code block 5001” and the symbols −S₂*S₁* transmittedthrough third and fourth antennas 5051 and 5053 serving as diversityantennas will be referred to as a “diversity antenna STTD code block5003”. The reference antenna STTD code block 5001 is multiplied by afirst orthogonal code OVSF1 (5005) by a multiplier 5007, and thenmultiplied by a scrambling code C_(SC) (5037) by a multiplier 5039, andthe resulting value is transmitted through the first antenna 5047. Forexample, the first orthogonal code OVSF1 (5005) has a chip rate of 256.In the same manner, the reference antenna STTD code block 5001 ismultiplied by the first orthogonal code OVSF1 (5005) by a multiplier5009, and then multiplied by the scrambling code C_(SC) (5037) by amultiplier 5041, and the resulting value is transmitted through thesecond antenna 5049.

Further, the diversity antenna STTD code block 5003 is multiplied by thefirst orthogonal code OVSF1 (5005) by a multiplier 5011, and thenmultiplied by the scrambling code C_(SC) (5037) by a multiplier 5043,and the resulting value is transmitted through the third antenna 5051.In the same manner, the diversity antenna STTD code block 5003 ismultiplied by the first orthogonal code OVSF1 (5005) by a multiplier5013, and then multiplied by the scrambling code C_(SC) (5037) by amultiplier 5045, and the resulting value is transmitted through thefourth antenna 5053.

Next, a receiver structure corresponding to the transmitter structureshown in FIG. 9 will be described with reference to FIG. 11. FIG. 11illustrates a structure of a transmit diversity receiver for estimatingcommon data according to another embodiment of the present invention.Two output signals shown in FIG. 11 can be represented by Equations (13)to (14) below. Specifically, Equation (13) represents a first datasymbol detection value ŝ₁, and Equation (14) represents a second datasymbol detection value ŝ₂.ŝ ₁ =ŝ ₁₁ +ŝ ₂₁  (13)ŝ ₂ =ŝ ₁₂ +ŝ ₂₂  (14)

In Equations (13) and (14), ŝ₁₁ and ŝ₁₂ indicate output signals of afirst STTD soft decoder 617, and ŝ₂₁ and ŝ₁₂ indicate output signals ofa second STTD soft decoder 619.

A signal received at an antenna 601 of the UE 203 is provided to adespreader 605 after it is converted to a baseband signal, and then,despread there with a scrambling code 603. The signal despread by thedespreader 605 is provided in common to an orthogonal despreader 609 andan orthogonal despreader 611. The orthogonal despreader 609 despreadsthe signal output from the despreader 605 using a first orthogonal codeOVSF1 (607) and the orthogonal despreader 611 despreads the signaloutput from the despreader 605 using a second orthogonal code OVSF2(613). The signal despread with the first orthogonal code OVSF1 issubjected to soft detection by the STTD soft decoder 617 using theleading two symbols of a channel estimation value output from a channelestimator 615, and the two resulting values are provided to adders 621and 623, respectively. The signal despread with the second orthogonalcode OVSF2 is subjected to soft detection by the STTD soft decoder 619using the following two symbols of the channel estimation value outputfrom the channel estimator 615, and the two resulting values areprovided to the adders 621 and 623, respectively. An added value by theadder 621 is output as a first data detection value, and an added valueby the adder 623 is output as a second data detection value. When thegain constant g (355) of the pilot channel is not identical to the gainconstant g (555) of the common data channel, the STTD soft decoder 617is constructed such that its output value is multiplied by a ratio of(gain constant g (555))/(gain constant g (355)) before it is added tothe output of the STTD soft decoder 619 by the adder 621. Likewise, theSTTD soft decoder 617 is constructed such that its output value ismultiplied by a ratio of (gain constant g (555))/(gain constant g (355))before it is added to the output of the STTD soft decoder 619 by theadder 623.

The structure of the transmit diversity receiver for estimating thecommon channel data using 2 orthogonal codes has been described withreference to FIG. 11. Next, a transmit diversity receiver structure forcommon data estimation, which corresponds to the transmitter structure,shown in FIG. 10, using a single orthogonal code will be described withreference to FIG. 12.

FIG. 12 illustrates a structure of a transmit diversity receiver forestimating common data using a single orthogonal code according toanother embodiment of the present invention. A signal received at anantenna 6001 of the UE 203 is provided to a despreader 6005 after it isconverted to a baseband signal, and then despread there with ascrambling code C_(SC) (6003). The signal despread by the despreader6005 is orthogonal-despread with a first orthogonal code OSVF1 (6007) byan orthogonal despreader 6008. The orthogonal despread signal isprovided to an STTD soft decoder 6017, which soft-detects the orthogonaldespread signal using leading 2 symbols ĥ_(A) and ĥ_(B) of a channelestimation signal output from a channel estimator 6015, and outputs thetwo resulting values as data detection values ŝ₁ and ŝ₂.

Now, an operation of the invention will be described in detail withreference to the accompanying drawings.

In general, the transmit antenna diversity system refers to a systemwhich transmits information through a plurality of antennas, so thateven if information received from a specific one of the antennas isdamaged, the receiver can receive the information through the otherantennas, thus increasing transmission efficiency. Therefore, in such atransmit antenna diversity system, the UE creates weights for maximalratio combining by measuring the antennas. As stated above, the closedloop mode is used to feed back the created weights to the UTRAN so thatthe UTRAN can assigns the weights, and the open loop mode is used tocombine the respective antenna signals received at the UE, using thecreated weights. The characteristics of the transmit antenna diversitysystem depend upon the number of the antennas applied for the diversity.For example, the system may have two or four or more antennas toimplement the transmit diversity.

However, when a UE operating in a two-antenna transmit diversity modeenters a service area of a UTRAN system supporting a four-antennatransmit diversity having first to fourth antennas, the UTRAN systempairs the first and second antennas and pairs the third and fourthantennas through signal processing so as to operate as if it providesthe service using two antennas. Meanwhile, when a UE supporting afour-antenna transmit diversity enters the service area of the UTRANsystem, the UTRAN system normally supports the four-antenna transmitdiversity by transmitting signals through the respective antennas.

A W-CDMA UTRAN supporting the two-antenna transmit diversity assigns twoorthogonal pilot symbol patterns to the respective antennas, so that theUE can measure the two different antenna channels. The UE measures thefirst antenna channel using the first orthogonal symbol pattern out ofthe two orthogonal symbol patterns, and measures the second antennachannel using the second orthogonal symbol pattern. However, thefour-antenna transmit diversity UTRAN transmits the pilot signals suchthat the four antenna channels can be separated. In order to enable theUE supporting the two-antenna transmit diversity to operate withoutmodification and to uniformly distribute the signal power to the fourantennas for the two-antennas diversity, the first and second antennasare paired to make an effective antenna A and the third and fourthantennas are paired to make an effective antenna B, as shown in FIG. 2.Although there are several methods for pairing (grouping) the twoantennas through signal processing, a method for transmitting the samesignal through the two antennas is typically used. The UE supporting thetwo-antenna diversity considers that the signals are received throughtwo antennas, i.e., the effective antenna A and the effective antenna B.

If a channel of the first antenna is represented by h₁, a channel of thesecond antenna is represented by h₂, a channel of the third antenna isrepresented by h₃ and a channel of the fourth antenna is represented byh₄, then a channel of the effective channel A is represented byh_(A)=h₁+h₂, and a channel of the effective channel B is represented byh_(B)=h₃+h₄. It is assumed that in light of the characteristic of thediversity channel, the channel h_(A) and the channel h_(B) have the samecharacteristics as the diversity channels of the two-antenna transmitdiversity. Accordingly, a UE for the four-antenna diversity systemperforms the diversity using the 4 channels of h₁, h₂, h₃ and h₄, and aUE for the two-antenna diversity system performs the diversity using thetwo channels of h_(A) and h_(B).

There are several methods for enabling the UE for the two-antennatransmit diversity to perform the diversity using the effective antennaA and the effective antenna B in the service area of the UTRANsupporting the four-antenna transmit diversity. A typically method is totransmit a first same signal through the first and second antennas forthe data to be transmitted through the effective antenna A, and alsotransmit a second same signal through the third and fourth antennas forthe data o be transmitted through the effective antenna B.

In case of the two-antenna STTD which is a kind of an open loop transmitdiversity, when providing the service with four antennas, the UTRANtransmits the original data through the effective antenna A, i.e., thefirst and second antennas, and transmits the diversity data through theeffective antenna B, i.e., the third and fourth antennas, for the UEsupporting the two-antenna transmit diversity. In case of two-antennaTxAA (Transmit Antenna Array) which is a kind of the closed looptransmit diversity, the UTRAN transmits a signal obtained by multiplyingtransmission data by a first weight through the effective antenna A,i.e., the first and second antennas, and transmits a signal obtained bymultiplying transmission data by a second weight through the effectiveantenna B, i.e., the third and fourth antennas.

The two-antenna diversity UE must measure the channel h_(A) obtained byadding h₁ and h₂, and the channel h_(B) obtained by adding h₃ and h₄, sothat the UTRAN pairs the channels by two when transmitting the pilotsymbol patterns. Table 1 below shows a pilot transmission standard fortwo antennas in the four-antenna transmit diversity system. When theUTRAN transmits the pilot symbol patterns as shown in Table 1, the UEobtains the paired channels. The pilot symbol patterns are orthogonalpilot symbol patterns used to distinguish the antennas. The orthogonalsymbol patterns are created with Walsh codes. In the W-CDMA system, thepilot signals are transmitted over a common pilot channel (CPICH), whichhas a unique channelization code. The UE measures the channel h_(A)obtained by adding h₁ and h₂ by correlating the signal received throughthe common pilot channel with a pattern #1, and measures the channelh_(B) obtained by adding h₃ and h₄ by correlating the received signalwith a pattern #2.

TABLE 1 Antenna Antenna Antenna Antenna Antenna Number #1 #2 #3 #4Channel h1 h2 h3 h4 Pilot Symbol Pattern Pattern #1 Pattern #1 Pattern#2 Pattern #2

A four-antenna transmit diversity UTRAN compatible with a UE for thetwo-antenna transmit diversity uses an additional common pilot channelfor channel measurement by a UE for the four-antenna transmit diversity.Herein, the existing common pilot channel will be referred to as a“first common pilot channel”, while the additional common pilot channelwill be referred to as a “second common pilot channel.” The four-antennatransmit diversity should measure all of the four antenna channels h₁,h₂, h₃ and h₄. If the four-antenna transmit diversity system of Table 1transmits the pilot signals in accordance with a standard of Table 2including the pilot transmission standard for the two-antenna transmitdiversity, four antenna channels are obtained by linearly combining ameasured result of the first common pilot channel with a measured resultof the second common pilot channel. When the first common pilot channelis received, a channel h_(A)=h₁+h₂ and a channel h_(B)=h₃+h₄ areobtained. When the second common pilot channel is received, a channelh_(C)=h₁−h₂ and a channel h_(D)=h₃−h₄ are obtained. Table 2 below showsa pilot transmission standard for two antennas in the four-antennatransmit diversity system.

TABLE 2 Antenna Antenna Antenna Antenna Antenna Number #1 #2 #3 #4Channel h1 h2 h3 h4 Pilot Symbol Pattern #1 #1 #1 −#1 #2 #2 #2 −#2 CPICH#1 #2 #1 #2 #1 #2 #1 #2

To be compatible with the two-antenna transmit diversity UE, thefour-antenna transmit diversity UTRAN groups the four antennas by two totransmit the signals through 2 effective antennas. The UE for thefour-antenna transmit diversity performs the diversity with four antennachannels. In order to enable the UE for the two-antenna transmitdiversity to operate as if it has two channels in the same method as theexisting method, the UTRAN system transmits the pilot symbol patternsaccording to the transmission standard of Table 2, using the firstcommon pilot channel and the second common pilot channel. Thus, the UEfor the four-antenna transmit diversity measures four antenna channelsthrough linear combination of the pilots.

In addition, in the W-CDMA system, common data is transmitted overcommon data channels (CDCHs). The common data channels have uniquechannelization codes and detect estimated data symbols for thetransmitted symbols by STTD decoding the signal received over the commondata channels, using an estimated value of the channel h_(A) obtained byadding h₁ and h₂ and an estimated value of the channel h_(B) obtained byadding h₃ and h₄. Table 3 below shows a common data transmissionstandard for two antennas in the four-antenna transmit diversity system.

TABLE 3 Antenna Antenna Antenna Antenna Antenna Number #1 #2 #3 #4Channel h1 h2 h3 h4 STTD Code Block Reference Reference DiversityDiversity Antenna Antenna Antenna Antenna Block Block Block BlockChannelization #3 #3 #3 #3 Code

A four-antenna transmit diversity UTRAN compatible with a UE for thetwo-antenna transmit diversity uses an additional common data channelfor channel measurement by a UE for the four-antenna transmit diversity.Herein, the existing common data channel will be referred to as a “firstcommon data channel”, while the additional common data channel will bereferred to as a “second common data channel.” The four-antenna transmitdiversity should measure all of the four antenna channels h₁, h₂, h₃ andh₄. If the data signals are transmitted in accordance with a standard ofTable 4 configured including the transmission standard of Table 3, atransmission symbol estimation value is calculated by linearly combininga measured result of the first common data channel with a measuredresult of the second common data channel. The received first common datachannel is restored to the transmitted symbol using an h_(A)=h₁+h₂channel estimation value and an h_(B)=h₃+h₄ channel estimation value.The received second common data channel is restored to the transmittedsymbol using an h_(C)=h₁−h₂ channel estimation value and an h_(D)=h₃−h₄channel estimation value. Herein, please note that #3 is only one ofseveral OVSF CODEs, which is different from #1 or #2 in table 4.

Table 4 below shows a common data transmission standard for 2 antennasin the four-antenna transmit diversity system.

TABLE 4 Antenna Antenna Antenna Antenna Antenna Number #1 #2 #3 #4Channel h1 h2 h3 h4 Common Data Symbol #1 #1 #1 −#1 #2 #2 #2 −#2 (STTD)Channelization Code #1 #2 #1 #2 #1 #2 #1 #2

In Table 4, #1 denotes a reference antenna coding block and #2 denotes adiversity antenna coding block.

When using the transmitter of FIG. 10 and the receiver of FIG. 12, thediversity system requires only one channelization code. Thus, the commondata channels received at the receiver are restored to the common datasymbols transmitted from the transmitter using the h_(A)=h₁+h₂ channelestimation value and the h_(B)=h₃+h₄ channel estimation value.

To be compatible with a UE for the two-antenna transmit diversity, thefour-antenna transmit diversity UTRAN groups the four antennas by two totransmit the signals through two effective antennas. The UE for thefour-antenna transmit diversity performs the diversity with four antennachannels. In order to enable the UE for the two-antenna transmitdiversity to operate as if it has two channels in the same method as theexisting method, the UTRAN transmits the common data according to thetransmission standard of Table 3, using the two common data channels.The UE for the four-antenna transmit diversity detects the signals inthe four-antenna diversity mode, using the received common data signals.

With reference to FIGS. 9 and 11, the transmit diversity system has beendescribed which transmits and receives the common data symbol patternsas well as the pilot symbol patterns according to the present invention.In addition, the transmit diversity system for transmitting andreceiving fixed physical channel symbol patterns through the open loopmode (STTD) can also be implemented in the same method as described inFIGS. 10 and 12.

As described above, when a UE using a transmit diversity technique whoseantennas is different in number from the antennas of the transmitdiversity technique supported by the UTRAN enters a service area of theUTRAN, the invention can uniformly distribute the transmission power tothe respective antennas by maintaining compatibility between thedifferent diversity techniques.

For example, if the UTRAN can service a maximum of 100 users, the UTRANprocesses 100/4 or 25 units of power per antenna for the four-antennatransmit diversity UE, and processes 100/2 or 50 units of power for thetwo-antenna transmit diversity UE. In accordance with the invention,however, the UTRAN may process a maximum of 100/4 power even for thetwo-antenna transmit diversity UE, thus making it possible to avoidusing the expensive RF element such as a power amplifier.

In addition, even in the case where there coexist a UE for thetwo-antenna transmit diversity and a UE for the four-antenna transmitdiversity, the system employing the four-antenna transmit diversitytechnique supports the pilot symbol pattern transmission so that the UEfor the four-antenna transmit diversity measures four channels, and theUE for the two-antenna transmit diversity measures two channels.Therefore, the UE for the two-antenna transmit diversity does notrequire an additional channel measurement device, and the UE for thefour-antenna transmit diversity has the minimized number of the channelmeasurement device.

Further, for the common data, the transmit diversity system has aneffect of the four-antenna transmit diversity and is compatible with theUE for the two-antenna transmit diversity.

Moreover, it is possible to implement a transmit diversity transmitterhaving antennas, the number of which is over four, e.g., a multiple offour, by separately applying the orthogonal code and the scrambling codeto the four-antenna transmit diversity. In addition, it is possible toimplement a transmit diversity system having various numbers of antennasas well as a transmit diversity system having the antennas, the numberof which is a multiple of four, by limiting signal transmission througha specific antenna.

In addition, by controlling transmission power of the respectiveantennas, it is possible to control the cell radiuses for the pilotsignals to be identical regarding a receiver employing a one-antennatransmit diversity, a receiver employing a two-antenna transmitdiversity, a receiver employing a four-antenna transmit diversity and areceiver employing a transmit diversity having a different number ofantennas.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A UTRAN (UMTS (Universal Mobile Telecommunication System) TerrestrialRadio Access Network) transmitter in a mobile communication systemhaving at least four antennas, comprising: a first adder connected to afirst antenna that adds a first spread signal, obtained by spreading afirst symbol pattern with a first orthogonal code, to a second spreadsignal obtained by spreading the first symbol pattern with a secondorthogonal code; a second adder connected to a second antenna that addsthe first spread signal to a third spread signal obtained by spreading afirst inverted symbol pattern obtained by phase-inverting the firstsymbol pattern with the second symbol pattern; a third adder connectedto a third antenna that adds a fourth spread signal, obtained byspreading a second symbol pattern being orthogonal with the first symbolpattern with the first orthogonal code, to a fifth spread signalobtained by spreading the second symbol pattern with the secondorthogonal code; a fourth adder connected to a fourth antenna that addsthe fourth spread signal to a sixth spread signal obtained by spreadinga second inverted symbol pattern obtained by phase-inverting the secondsymbol pattern with the second orthogonal code; a fifth adder connectedto a fifth antenna that adds a seventh spread signal obtained byspreading the first symbol pattern with a third orthogonal code, to aneighth spread signal obtained by spreading the first symbol pattern witha fourth orthogonal code; a sixth adder connected to a sixth antennathat adds the seventh spread signal to a ninth spread signal obtained byspreading the first inverted symbol pattern with the fourth orthogonalcode; a seventh adder connected to a seventh antenna that adds a tenthspread signal, obtained by spreading the second symbol pattern with thethird orthogonal code, to an eleventh spread signal obtained byspreading the second symbol pattern with the fourth orthogonal code; andan eighth adder connected to an eighth antenna that adds the tenthspread signal to a twelfth spread signal obtained by spreading thesecond inverted symbol pattern with the fourth orthogonal code.
 2. TheUTRAN transmitter as claimed in claim 1, wherein the first orthogonalcode is different from the third orthogonal code and the secondorthogonal code is different from the fourth orthogonal code.
 3. TheUTRAN transmitter as claimed in claim 1, wherein when the firstorthogonal code is identical to the third orthogonal code and the secondorthogonal code is identical to the fourth orthogonal code, then a firstscrambling code applied to output signals of the first to fourthantennas is set to be different from a second scrambling code applied tooutput signals of the fifth to eighth antennas.
 4. The UTRAN transmitteras claimed in claim 1, wherein the transmitter selects only the numberof antenna's transmission of specific signals among the output signalsof the first to eighth antennas, when the number of antennas is lessthan eight.
 5. The UTRAN transmitter as claimed in claim 1, wherein eachof the symbol pattern is one of a pilot symbol pattern and a data symbolpattern.
 6. A data transmission method in a UTRAN (UMTS (UniversalMobile Telecommunication System) Terrestrial Radio Access Network)transmitter for a mobile communication system having at least fourantennas, comprising the steps of: adding a first spread signal,obtained by spreading a first symbol pattern with a first orthogonalcode, to a second spread signal, obtained by spreading the first symbolpattern with a second orthogonal code, to generate a first added signaland transmitting the first added signal through a first antenna; addingthe first spread signal to a third spread signal obtained by spreading afirst inverted symbol pattern obtained by phase-inverting the firstsymbol pattern with the second orthogonal code, to generate a secondadded signal and transmitting the second added signal through a secondantenna; adding a fourth spread signal obtained by spreading a secondsymbol pattern, being orthogonal with the first symbol pattern with thefirst orthogonal code, to a fifth spread signal, obtained by spreadingthe second symbol pattern with the second orthogonal code, to generate athird added signal and transmitting the third added signal through athird antenna; adding the fourth spread signal to a sixth spread signalobtained by spreading a second inverted symbol pattern obtained byphase-inverting the second symbol pattern with the second orthogonalcode, to generate a fourth added signal and transmitting the fourthadded signal through a fourth antenna; adding a seventh spread signal,obtained by spreading the first symbol pattern with a third orthogonalcode, to an eighth spread signal, obtained by spreading the first symbolpattern with a fourth orthogonal code, to generate a fifth added signaland transmitting the fifth added signal through a fifth antenna; addingthe seventh spread signal to a ninth spread signal obtained by spreadingthe first inverted symbol pattern with the fourth orthogonal code, togenerate a sixth added signal and transmitting the sixth added signalthrough a sixth antenna; adding a tenth spread signal, obtained byspreading the second symbol pattern with the third orthogonal code, toan eleventh spread signal, obtained by spreading the second symbolpattern with the fourth orthogonal code, to generate a seventh addedsignal and transmitting the seventh added signal through a seventhantenna; and adding the tenth spread signal to a twelfth spread signalobtained by spreading the second inverted symbol pattern with the fourthorthogonal code, to generate a eighth added signal and transmitting theeighth added signal through an eighth antenna.
 7. The data transmissionmethod as claimed in claim 6, wherein the first orthogonal code isdifferent from the third orthogonal code and the second orthogonal codeis different from the fourth orthogonal code.
 8. The data transmissionmethod as claimed in claim 6, wherein when the first orthogonal code isidentical to the third orthogonal code and the second orthogonal code isidentical to the fourth orthogonal code, then a first scrambling codeapplied to output signals of the first to fourth antennas is differentfrom a second scrambling code applied to output signals of the fifth toeighth antennas.
 9. The data transmission method as claimed in claim 6,further comprising the step of controlling transmission of specificsignals among the output signals of the first to eighth antennas whenthe number of antennas is less than eight.
 10. A UE (User Equipment)receiver in a mobile communication system, wherein the UE receiverreceives signals transmitted from a UTRAN transmitter supporting atransmit diversity technique having at least four antennas, comprising:a plurality of despreaders for generating a first despread signaldespread using a first orthogonal code and a first symbol pattern of thereceived signals, generating a second despread signal despread using thefirst orthogonal code and a second symbol pattern being orthogonal withthe first symbol pattern, generating a third despread signal dispreadusing a second orthogonal code being orthogonal with the firstorthogonal code and the first symbol pattern, generating a fourthdespread signal despread using the second orthogonal code and the secondsymbol pattern, generating a fifth despread signal despread using athird orthogonal code and the first symbol pattern, generating a sixthdespread signal despread using the third orthogonal code and the secondsymbol pattern, generating a seventh despread signal despread using afourth orthogonal code and the first symbol pattern, and generating aneighth despread signal despread using the fourth orthogonal code and thesecond symbol pattern; and a plurality of adders for generating a firstchannel estimation signal by adding the first despread signal to thethird despread signal, generating a second channel estimation signal byadding the second despread signal to the fourth despread signal,generating a third channel estimation signal by subtracting the thirddespread signal from the first despread signal, generating a fourthchannel estimation signal by subtracting the fourth despread signal fromthe second despread signal, generating a fifth channel estimation signalby adding the fifth spread signal to the seventh despread signal,generating a sixth channel estimation signal by adding the sixthdespread signal to the eighth despread signal, generating a seventhchannel estimation signal by subtracting the seventh despread signalfrom the fifth despread signal, and generating an eighth channelestimation signal by subtracting the eighth despread signal from thesixth despread signal.
 11. The UE receiver as claimed in claim 10,wherein the symbol pattern is one of a pilot symbol pattern and a datasymbol pattern.
 12. A data reception method in a UE (User Equipment)receiver for a mobile communication system, wherein the UE receiverreceives signals transmitted from a UTRAN transmitter supporting atransmit diversity technique having at least four antennas, comprisingthe steps of: despreading the received signals into a first despreadsignal using a first orthogonal code and a first symbol pattern,despreading the received signals into a second despread signal using thefirst orthogonal code and a second symbol pattern being orthogonal withthe first symbol pattern, despreading the received signals into a thirddespread signal using the second orthogonal code and the first symbolpattern, despreading the received signal into a fourth despread signalusing the second orthogonal code and the second symbol pattern,despreading the received signals into a fifth despread signal using athird orthogonal code and the first symbol pattern, despreading thereceived signals into a sixth despread signal using the third orthogonalcode and the second symbol pattern, despreading the received signal intoa seventh despread signal using a fourth orthogonal code and the firstsymbol pattern, and despreading the received signals into an eighthdespread signal using the fourth orthogonal code and the second symbolpattern; and estimating a first channel signal by adding the firstdespread signal to the third despread signal, estimating a secondchannel signal by adding the second despread signal to the fourthdespread signal, estimating a third channel signal by subtracting thethird despread signal from the first despread signal, estimating afourth channel signal by subtracting the fourth despread signal from thesecond despread signal, estimating a fifth channel signal by adding thefifth spread signal to the seventh despread signal, estimating a sixthchannel signal by adding the sixth despread signal to the eighthdespread signal, estimating a seventh channel signal by subtracting theseventh despread signal from the fifth despread signal, and estimatingan eighth channel signal by subtracting the eighth despread signal fromthe sixth despread signal.
 13. The data reception method as claimed inclaim 12, wherein the symbol pattern is one of a pilot symbol patternand a data symbol pattern.